iPhone switching carrier by itself

[GGarcia411]

Okay I'm gonna explain this with as much detail as possible. I have an unlocked iPhone 4S that I am using with T-Mobile. Sometimes at random (mostly places where my signal is weak, like the outskirts of town) the carrier switches from T-Mobile to AT&T and it says 4G. It was an AT&T iPhone before I had it unlocked. I'm pretty sure it's impossible to get 4G on a 4S. When I tried to load a page or anything using data, it would not load and it would give me an error. But I was able to make/receive calls. After a while it went back to normal and the data worked again. I'm just wondering what is going on. Any help would be appreciated! Sorry about the carrier changes, I was using Zeppelin.

I was going to upload screenshots but they wont all fit. This is a link to the screenshots that I uploaded to mediafire
http://www.mediafire.com/?k74d9g5cakqaj

 

[Applejuiced]

AT&T and Tmobile have an agreement to let eachother roam on their network and viceversa.
So if there is no connection to Tmobile your phone will switch and connect to AT&T so you can still get service.
Not sure why data doesnt work but it should.
And yes you can get 4G on AT&T with a 4S. Its what they call their HSPA+ network and mostly a marketing gimmick.
Its not real LTE, just a faster 3G that they call 4G.

 

[GGarcia411]

You just blew my mind ._. I didn't know any of that, thanks for the reply!

 

[Applejuiced]

Glad to assist